Telephone diaphragm



Dec. 1, 192 1,563,512 L. 'R. M DONALD I TELEPHONE DIAPHRAGM Filed March 7 1924 amawtoz,

latented Dec. 1, 1925.

UNITE stares PATENT oFFrca.

TELEPHONE DIAPHRAGM.

Application filed March 7, 1924. Serial No. 697,434.

T 0 all whom it may concern:

Be. it known that I, LnsLrn R. I/ICDONALD, a citizen of the United States, residing at lVestmount, Province of Quebec, Dominion of Canada, have invented certain new and useful Improvements in Telephone Diaphragms, of which the following is a specification.

My invention relates to the improvements in electrically sensitive diaphragms which are used in the transmission and reproduction of sound by means of telephone instruments; and the object of my invention is to make these diaphragms more sensitive and more delicately responsive to the sound waves and electrical impulses by which they are influenced. In doing this I make use both of the direct pull of electromagnets, within the magnetic field of but out of contact with which the diaphragm is placed, and also of the capacity of metals to expand and contract under the varying influences of a magnetic field, using these features to sup plement each other, and to thereby increase the sensitiveness and efiiciency of a diaphragm.

In the drawing Fig. l is an elevation of a telephone receiver, partly in vertical section, and sl'iowing one of my improved diaphragms in position; Fig. 2 is a view look ing down on Fig. 1, and also partly in section; Fig. 3 is a plan view of a diaphragm, also partly in section; and Fig. 4 is a view similar to Fig. 1, showing a modified form of a diaphragm.

In all the figures similar parts are designated' by similar reference numerals.

The telephone instrument 1 can be of a conventional type, provided with the usual keeper element or cap 2 and electromagnets 3.

The diaphragm 4 is made of a thin plate of two or more metals of varied capacities for expansion and contraction under the influence of electricity. Preferably this is accomplished by depositing a coating of one metal upon a disk formed of another metal. Thus if the one portion, as 5, of the disk is of steel, and upon this is deposited a layer of cobalt, the cobalt will contract and the steel will expand under the influence of a magnetic field, so that the diaphragm will be dished on the cobalt side more markedly than would be the case if the steel only was employed. And if the layer 6 is of nickel, I

the nickel will contract more than cobalt and the diaphragm will be concaved on the nickel side, more markedly than would be the case if a cobalt-steel disk was used.

This arrangement-will give a greater play to the disk, and will increase its efliciency in transmitting sound.

"Such diaphragms may be used in ordinary telephone transmitters without any change therein, with the result of increasing the capacity of the instruments for the satisfactory transmission of sound.

In Fig. 4 I have shown a disk formed of three metals instead of two, the layer 7 being of a different responsiveness to an electric field than either of the layers 5 and 6.

Thus if 5 is of steel, 6 is cobalt, and 7 is nickel, the convexing of the diaphragm toward the electromagnets will be greater than would be the case if only two layers of metal were used; for the contraction of the cobalt will be supplemented by the contraction of the nickel, and the sensitiveness of the diaphragm will be to that extent increased.

It will be understood that the combinations of metals used in the diaphragm may be varied, from those mentioned, without departing from the principle of forming the diaphragm of layers of two or more metals of varying expansibility and contractability under the influence of a magnetic field, the diaphragm being held freely by its surrounding edge.

The actions of steel, and cobalt, which I have mentioned, are those which occur under the milder stages of inference of a magnetic field. As the strength of the field is increased, steel reaches a point beyond which it contracts, while cobalt reaches a point where it expands. And these characterlstics of cobalt and steel must be taken into account in connection with the strength of the particular magnetic field, in deciding upon the most desirable form to use in connection with any particular telephone instrument.

of a diaphragm composed of a plurality of layers of metal, differing one from another in capacity for expansion and. contraction under the influence of electricity, means for producing an electric field, and means for holding the disk in the electric field out of 15 contact with the electric mechanism.

LESLIE R. MCDONALD. 

